The Anionic Zirconocene Trihydride:  [Cp*₂ZrH₃]^-

Abstract

Synthetic pathways to several salts of the anion [Cp*2ZrH3]- have been developed. Reaction of Cp*2ZrH2 (3) prepared from [Cp*2Zr(N2)]2(μ-N2) (2), with KH in THF, afforded [Cp*2ZrH3]K (1) in a 74% yield. In a similar manner, addition of LiH gave [Cp*2ZrH3]Li (4). While this synthetic pathway provides reproducible routes to 1and 4, purification of 2 is problematic. Another preparation involving the reaction of Cp*2ZrCl2 with 3 equiv of n-BuLi under H2 affords 4·0.5(LiCl·THF). Alternatively, reaction of Cp*2ZrCl2 with LiAlH4 afforded the species Cp*2ZrH(μ2-H2AlH2) (5) in virtually quantitative yield. Subsequent reaction of 5 with n-BuLi afforded the direct and high-yield conversion to 4. Deuteration and NMR studies infer attack of BuLi occurs at the Al center exclusively prompting transfer of a hydride to Zr and liberation of the Zr trihydride anion. Variable-temperature 1H NMR spectra and H/D scrambling experiments for 4 and 4- d 3 are consistent with the hydride exchange process mediated by ion pairing while T 1 studies infer a classical trihydride formulation is appropriate. Crystallographic studies of 4·0.5(LiCl·THF), 5, and 4 also affirm cation−anion pairing in 4 and 4·0.5(LiCl·THF) and hydride bridging between Al and Zr in 5.

Dehydrogenative Bond-Forming Catalysis Involving Phosphines

“…A simple catalyst precursor, [Cp* 2 ZrH 3 ] -(1), was prepared via KH reduction of Cp* 2 ZrCl 2 and structurally characterized (eq 2) [54,55]. In this initial report, the potassium or lithium salt of complex 1 was demonstrated to catalytically oligomerize PhPH 2 , CyPH 2 , and MesPH 2 with the predominant product in all three cases being the cyclic pentamer (PR) 5 (eq.…”

2001 Alcan Award LectureFrom academic research to industrial applications and back again

“…Subsequently in 1997, we described the related sequence of reactions involving Cp* 2 ZrCl 2 with LiAlH 4 followed by treatment with BuLi (Scheme 1) (5). This synthetic route proceeds through the isolable intermediate [(Cp* 2 ZrH(AlH 4 )] 2 , ultimately giving the threefold symmetric species [(Cp* 2 ZrH 3 )Li] 3 in all but quantitative yield (Fig.…”

“…While the resulting reaction results in several products as evidenced by 31 P NMR spectroscopy, two products were crystallized and structurally characterized. One of the products is the Zr 4 cluster (Cp*Zr) 4 (µ-Cl) 5 (Cl)(µ-CH) 2 (Fig. 10) (18).…”

Zirconium - Phosphorus Chemistry: Strategies in Syntheses, Reactivity, Catalysis, and Utility

“…[116] Subsequently, the efficient and almost quantitative synthesis of the Li American Chemical Society 1997. [117] analogue 123 was reported (Figure 7). [117] The presence of 1 % of this compound was found to effect the catalytic dehydrocoupling of primary phosphanes at 80 ± 100 8C for 24 h to give 124.…”

“…[117] analogue 123 was reported (Figure 7). [117] The presence of 1 % of this compound was found to effect the catalytic dehydrocoupling of primary phosphanes at 80 ± 100 8C for 24 h to give 124. Stoichiometric reactions of 123 with phosphanes led to the isolation of the complexes 125 and 126; this implies the intermediacy of these species in the catalytic cycle.…”